Early reports said three people were dead, as rescue workers scrambled to aid thousands of residents marooned in tent cities since a massive earthquake devastated the city nearly three years ago.

A statement late Saturday from the U.S. National Hurricane Center placed the storm over eastern Cuba, moving to the northwest at about 30 kilometers an hour. It is expected to gain hurricane force as it moves toward the Florida Keys, the Gulf of Mexico and the U.S. mainland Sunday.

The center has issued hurricane warnings for the west coast of Florida that includes the city of Tampa -- the site of next week's four-day Republican national convention.

Late Saturday, authorities moved the convention start from Monday to Tuesday, in a move designed to protect attendees from possible harm as the storm moves northward.

In the Haitian capital, Red Cross worker France Hurtubise said most tents held up at one camp, but some were damaged.

"The populations are extremely worried because some of the tents are leaking, so we have to respond to this which is quite urgent," Hurtubise said.

She also voiced concern about the potential for mudslides on the area's vulnerable population.